Help with layers

I am new to Photoshop and require some assistance with an image I’m trying to edit.

The image is of a house and is made up of two separate images – one correctly exposed for the house, the other correctly exposed for the sky.

I opened both images in photoshop and selected the one of the house as my base or background image. I then selected, copied and pasted the other image (sky) on top of my base image (house).

After adding a layer mask I then used the brush tool to brush the areas I wanted to blend.

I now have the house and the sky I want in one image but I want to individually adjust the levels for each part of the image.

I want to do this by adding an adjustment layer so as my alterations can be easily undone without permanently altering or degrading my image.

If I add an adjustment layer it alters both images simultaneously. The only way I can adjust the levels for each image separately is by clicking on each layer and adjusting the levels that way but this will not allow me to amend any changes I make at a later date.

Any help much appreciated – thank you in advance.

Lee

post the images you may get better help if members see what you are doing